There has been significant progress on the fundamental science and technological applications of complex oxides and multiferroics. Among complex oxide thin films, barium strontium titanate (BST) has become the material of choice for room-temperature-based voltage-tunable dielectric thin films, due to its large dielectric tunability and low microwave loss at room temperature. BST thin film varactor technology based reconfigurable radio frequency (RF)/microwave components have been demonstrated with the potential to lower the size, weight, and power needs of a future generation of communication and radar systems. Low-power multiferroic devices have also been recently demonstrated. Strong magneto-electric coupling has also been demonstrated in different multiferroic heterostructures, which show giant voltage control of the ferromagnetic resonance frequency of more than two octaves. This manuscript reviews recent advances in the processing, and application development for the complex oxides and multiferroics, with the focus on voltage tunable RF/microwave components. The over-arching goal of this review is to provide a synopsis of the current state-of the-art of complex oxide and multiferroic thin film materials and devices, identify technical issues and technical challenges that need to be overcome for successful insertion of the technology for both military and commercial applications, and provide mitigation strategies to address these technical challenges. V C 2013 AIP Publishing LLC.

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Piezoelectric properties of epitaxial (001) barium strontium titanate (BST) films are computed as functions of composition, misfit strain, and temperature using a non-linear thermodynamic model. Results show that through adjusting in-plane strains, a highly adaptive rhombohedral ferroelectric phase can be stabilized at room temperature with outstanding piezoelectric response exceeding those of lead based piezoceramics. Furthermore, by adjusting the composition and the in-plane misfit, an electrically tunable piezoelectric response can be obtained in the paraelectric state. These findings indicate that strain engineered BST films can be utilized in the development of electrically tunable and switchable surface and bulk acoustic wave resonators.

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A systematic study of Au/Zn/Au ohmic contacts to Be‐implanted p‐type normalGaAs by rapid thermal alloying is presented. The processing conditions, such as zinc composition and temperature‐time cycle, are optimized. For the peak hole concentration, about Nnormala=3×1017 cm−3 , contact resistivity as low as 3.3×10−6 normalΩ cm2 is obtained. The microstructure of the contact is investigated using SEM, EDXA, AES, and XRD measurements in order to explore the correlation of the structural information with electrical characteristics represented by contact resistivity. It is found that during alloying, the normalGaAs layer near the interface is decomposed due to Ga and As outdiffusion, enhanced by Au interdiffusion. Ga diffuses to the contact surface in a much larger extent than As does. The interaction of Au and Ga, which produces α‐normalAuGa phase, plays a key role in the formation of alloyed ohmic contacts to normalGaAs . The rapid thermal processing technique provides better control of Au‐Ga reaction, as well as limited dissolution of the normalGaAs surface, which makes the optimum ohmic contact possible. The present work has demonstrated that rapid thermal alloying offers obvious advantages over the conventional furnace alloying process, including lower contact resistivity, better interface morphology by limiting interfacial liquid phase reaction, and controlled shallow penetration depth.

We have examined the zero-bias conductance peak that is often found in high-temperaturesuperconductor tunnel-junction spectra. We have also measured the Bi-Sr-Ca-Cu-O thin-film energy gap. The zero-bias conductance peak can be explained in terms of quasiparticle tunneling, phase diffusion, and a supercurrent. The implications of this model are discussed.

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